Atactic or amorphous polypropylene (APP), as used herein, is a substantially stereo-irregular, non-crystalline propylene polymer.
For years, APP has received attention in the polypropylene industry solely because of the difficulties created by its presence as a byproduct in the polymerization of propylene to isotactic polypropylene (IPP). In fact, APP was once regarded as a disposal problem, rather than as a marketable byproduct. Since the discovery of polypropylene, research efforts have therefore focused exclusively on the elimination of the unwanted APP byproduct from IPP production processes. These efforts have been successful and current catalyst technologies reduce APP output to levels where its separation from the IPP product by solvent extraction is unnecessary.
Ironically, however, within the last ten years, APP has gained a considerable market in the United States and abroad. Its uses range from mixing with bitumen to produce modified asphalt used in roofing materials and road paving, to adhesives, paper laminating and cable flooding. Today, APP is no longer a disposal problem. Rather, as the most advanced catalyst technologies for IPP production steadily replace the old, APP is quickly becoming a problem of severe shortage.